Abstract: A pulp mixing apparatus includes a rotor shaft within a housing having a curvilinear inner wall circumferentially disposed about the rotor. A plurality of radially extending, wedge-shaped vanes are rigidly mounted on the rotor and intermesh with a plurality of housing vanes, likewise wedged-shaped, such that in combination, as the rotor vanes are moved into proximity with the stationary housing vanes, a mixing substance is subjected to a compressive and subsequently to a decompressive force whereupon the mixing substance is homogeneously and thoroughly mixed.